I am using an 500w electric hoist/motor that runs off 230v ~ 50Hz mains supply. This has a 3-way switch UP/off/DOWN I would like to connect this switch to the arduino digital inputs effectively just to send the UP/off/Down information to a computer.

What resistor should I use with this kind of power so I don't kill myself and the arduino board?

I am using an 500w electric hoist/motor that runs off 230v ~ 50Hz mains supply. This has a 3-way switch UP/off/DOWN I would like to connect this switch to the arduino digital inputs effectively just to send the UP/off/Down information to a computer.

What resistor should I use with this kind of power so I don't kill myself and the arduino board?

I wouldn't use just resistors at all, too much risk of damage or injury. I would use opto-isolators to monitor the voltage on the switches and wire the info to the arduino. However this clearly falls into the 'if you have to ask you probably shouldn't mess with it" kind of project, so I will leave it at that.

If the Arduino is to be located close to the switch or to the motor wires, then another possibility is capacitive sensing. Wrap sense wires around the wires feeding power to the motor, and connect those sense wires to Arduino inputs, using high-value pulldown resistors.

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I am using an 500w electric hoist/motor that runs off 230v ~ 50Hz mains supply. This has a 3-way switch UP/off/DOWN I would like to connect this switch to the arduino digital inputs effectively just to send the UP/off/Down information to a computer.

What resistor should I use with this kind of power so I don't kill myself and the arduino board?

One thought might be an on-off-on double pole switch, and wire one pole for A/C, and the other pole for the Arduino. I would want to test it with a multimeter first to make sure there is no current leakage between the two poles.

Alternatively, I could imagine putting two different colored A/C leds on the up/down circuits and use a color sensor on the Arduino.